Lifer, let me give a couple of examples of Benefits madness.
Your not fit for work so claim ESA. Your other half does not work but is physically prefectly fit. You can claim for them. They do not have to sign on.
You are disabled, cannot care for yourself and receive High Rate DLA Care. Because of this, your partner can claim Carers Allowance for looking after you. But your partner too is disabled, cannot care for themselves and receives High Rate DLA Care. So you can claim Carers Allowance for looking after them. In other words, two people who cant look after themselves, are perfectly entitled to claim for looking after each other.
And that’s the tip of the iceberg.